Figure 2-9 Current Measurements - Keithley 6512 Instruction Manual

To measure current with the Model 6512, use the following
procedure:
1. Turn on the power, and allow the instrument to warm up
for at least two hours to obtain rated accuracy.
2. Select the current mode by pressing the AMPS button on
the front panel. Set the V, Ω/ GUARD switch to OFF.
3. To achieve rated accuracy, select the 2pA range, zero the
instrument by enabling zero check and then pressing the
ZERO CORRECT button. After zero correction, select
the desired range, or use auto-ranging if desired.
OFF
VΩ, GUARD
I S
Figure 2-9
Current measurements
TRIAX CABLE
INPUT
ON
MODEL 6512
INPUT
AMPLIFIER
Z F
INPUT
HI
LO
S
GND
PREAMP
OUT
COM
4. Connect a suitable triax cable to the rear panel INPUT
jack. Connect the other end of the circuit to be measured
as shown in Figure 2-9. Shielding will be required for
low-level measurements. Connect the shield to input
low.
5. Disable zero check, and allow the reading to settle.
6. Read the current value directly from the display. The ex-
ponent may be placed either in the alpha or numeric
modes, as described in paragraph 2.5.
HI
LO
A. CONNECTIONS
RANGING
AMPLIFIER
100Ω
B. EQUIVALENT CIRCUIT
Operation
I S
MEASURED
CURRENT
SHIELD
RECOMMENDED
BELOW 1µA
TO A/D
CONVERTER
2V ANALOG
OUTPUT
S
2-13